Personally i generally dislike one company taking over the other, despite what is announced in press releases, in most cases it does not turn out for the better for the end consumer at the end. There are few exceptions to the rule of course.
That said, i´d still also make a seperation between single platform companies buying other single platform companies and the other case of a single platform holder buying out what was a multi platform provider before.
For Apple it would be huge to buy Sony, EA or Unity; for users of hardware/ software made by these companies it could be a disaster, since, well, it would probably mean that the stuff wouldn´t be available anymore other on Apple devices.
Something like this topic is really a total wild speculation topic until there are more solid facts.
And since we´re on a wild speculation topic, well, i´d go with saying that probably UT, EA and Sony could actually all be quite interesting for Apple, all for different reasons.
Buying EA would give them a way more powerful stance in the games business, they´d secure getting a lot more “AAA” and “casual” games while at the same time also having control over their contenders suddenly getting way less of those.
Buying Unity (if UT was even for sale) would of course give them a great game creation middleware for the iOS platforms, while again ensuring that their contenders don´t get that anymore.
Buying Sony would give them a lot of bulk (i don´t see how they´d for example want to continue to sell PS3s then) but also A LOT of force and content in many of the sectors they are active in. Like for example one could dream up a new gen of bravia tvs has the apple tv built in. Or hey, there was that kinda big catalogue and might Sony had in the movie and music industry, no? Would be nice to have more direct access and control over that 
Yeah, can be fun to speculate wildly, will also be interesting to talk about the facts if it ever comes to that state =)
To end on a more realistic note: With the size and domination Apple gets to in various sectors i´d find it unlikely that they´d actually get it approved without issues to swallow up a company in the size of Sony or EA, since it could in some areas get seen as getting to monopoly state to some extend.